Particle-size analysis is a standard type of industrial test which is performed on a wide variety of materials. Many bulk particulate items of commerce are sold according to some predetermined particle size requirement or classification. In addition, size classification data is frequently used as a control in various manufacturing processes. Such classification is usually referred to as a "screen analysis," a term chosen from the laboratory method of determining the particle size distribution of a sample. In that type of analysis, the sample to be analyzed is sifted on or through a plurality of sequentially graded screens (rom coarser to finer) and thereby divided into a plurality of size fractions. The size fractions are weighed and those weights are used to calculate a particle size or screen analysis, which is typically expressed in terms of the weight percentages of the size ranges retained on the respective screens.
Particle-size analyzers are commercially available. Rotex, Inc. sells an automatic particle-size analyzer under the trademark GRADEX, and U.S. Pat. Nos. 4,487,323 and 4,797,204 show polygonal drum-type automatic particle-size analyzers. A feature of automatic particle-size analyzers is a weighing scale which receives the sequential size fractions from the screening portion of the analyzer and indicates the weight thereof for use in calculating the particle size distribution of the sample. Once the size distribution analysis has been completed, the sample must be removed or cleared from the scale prior to the next analysis. Heretofore, this has been accomplished by manually removing the scale weighing pan and emptying the contents thereof and/or sweeping the contents from the pan. Such procedures are cumbersome, time consuming and inefficient. There is clearly a need for an efficient, expeditious means for clearing particulate matter from the weighing pans in automatic particle-size analyzers.